U.S. patent application number 10/056681 was filed with the patent office on 2003-07-24 for covered segmented stent.
Invention is credited to Diaz, Pedro L., Johnson, Kirk.
Application Number | 20030139797 10/056681 |
Document ID | / |
Family ID | 22005947 |
Filed Date | 2003-07-24 |
United States Patent
Application |
20030139797 |
Kind Code |
A1 |
Johnson, Kirk ; et
al. |
July 24, 2003 |
Covered segmented stent
Abstract
A covered stent comprising individual stent rings alternately
loaded inside and outside of the covering material, wherein the
rings are not connected to adjacent rings along the longitudinal
axis.
Inventors: |
Johnson, Kirk; (Weston,
FL) ; Diaz, Pedro L.; (Pembroke Pines, FL) |
Correspondence
Address: |
AUDLEY A. CIAMPORCERO JR.
JOHNSON & JOHNSON
ONE JOHNSON & JOHNSON PLAZA
NEW BRUNSWICK
NJ
08933-7003
US
|
Family ID: |
22005947 |
Appl. No.: |
10/056681 |
Filed: |
January 24, 2002 |
Current U.S.
Class: |
623/1.13 |
Current CPC
Class: |
A61F 2002/072 20130101;
A61F 2/89 20130101; A61F 2/07 20130101; A61F 2002/075 20130101 |
Class at
Publication: |
623/1.13 |
International
Class: |
A61F 002/06 |
Claims
What is claimed is:
1. A covered stent comprising individual stent rings alternately
loaded inside and outside a covering material, wherein the rings
are not connected longitudinally.
2. The stent of claim 1 wherein the covering material is selected
from the group consisting of ePTFE and PET.
3. The stent of claim 1 wherein the stent rings loaded inside the
covering material are stronger than the stent rings loaded outside
the covering material.
4. The stent of claim 1 wherein some of the stent is uncovered to
aid in anchoring the vessel.
5. The stent of claim 1 wherein foreshortening is reduced in
comparison to a longitudinally connected stent.
6. The stent of claim 1 wherein there are no perforations through
the covering material.
7. The stent of claim 1 where the stent rings loaded inside the
covering are larger in their unconstrained state than the stents
loaded on the outside of the covering.
8. The stent of claim 1 where gaps between alternating stent rings
when expanded are of sufficient length to prevent touching of the
stent structures when they are crimped to the diameter at which
they are delivered.
9. The stent of claim 1 where the features of the adjacent stent
rings are aligned so that they do not interfere with one another
when the composite stent is placed in a bend.
10. The stent of claim 1 wherein the covering material is selected
from the group consisting of ePTFE, PET, UHMWPE (ultra high
molecular weight polyethylene), polyester polyarylate, and PEEK
(polyester ether ketone).
Description
FIELD OF THE INVENTION
[0001] The present invention generally relates to medical devices,
particularly stents and covered stents. More particularly, the
present invention is directed to a covered stent comprising
individual stent rings loaded inside and outside of the covering
material.
BACKGROUND OF THE INVENTION
[0002] As background to a discussion of stents, one notes that in
the 1970s, the technique of percutaneous transluminal coronary
angioplasty (PTCA) was developed for the treatment of
atherosclerosis. Atherosclerosis is the build-up of fatty deposits
or plaque on the inner walls of a patients arteries; these lesions
decrease the effective size of the artery lumen and limit blood
flow through the artery, prospectively causing a myocardial
infarction or heart attack if the lesions occur in coronary
arteries that supply oxygenated blood to the heart muscles. The
term stenosis refers to a narrowing or restriction in the diameter
of a tubular structure, such as an artery. As a separate point, the
application of balloon angioplasty to certain blood vessels has
been limited by the risk of forming emboli during the procedure.
For example, when angioplasty is applied to lesions in the carotid
artery, there is the possibility of dislodging plaque from the
lesion, which can enter the various arterial vessels of the brain
and cause permanent brain damage.
[0003] In the angioplasty procedure, a guide wire is inserted into
the femoral artery and is passed through the aorta into the
diseased coronary artery. A catheter having a balloon attached to
its distal end is advanced along the guide wire to a point where
the sclerotic lesions limit blood flow through the coronary artery.
The balloon is then inflated, compressing the lesions radially
outward against the wall of the artery and substantially increasing
the size of its internal lumen, to improve blood circulation
through the artery.
[0004] A stent is a generally longitudinal tubular device formed of
biocompatible material, and is useful in the treatment of stenoses,
strictures or aneurysms in body vessels such as blood vessels.
These devices are implanted within the vessel to reinforce
collapsing, partially occluded, weakened or abnormally dilated
sections of the vessel. Stents are typically employed after
angioplasty of a blood vessel to prevent restenosis of the diseased
vessel. While stents are most notably used in blood vessels, stents
may also be implanted in other body vessels such as the urogenital
tract and the bile duct. Stents generally include an open flexible
configuration. This configuration allows the stent to be inserted
through curved vessels. Furthermore, the stent configuration allows
the stent to be configured in a radially compressed state for
intraluminal catheter implantation.
[0005] In the present time, it is the case that stents are
increasingly being used in place of or in addition to PTCA for
treatment of atherosclerosis, with the intent of minimizing the
need to repeatedly open an atherosclerotic artery. In fact, the
passage through the atherosclerotic artery is so small, that the
area of a stenosis often needs to be predilated with a small and
low profile balloon in order to be able to position the stent
delivery device and to deliver a self-expandable stent at the
desired location of the stenosis. The need to predilate the artery
necessitates the passage of a low profile balloon through the area
of stenosis, dilatation of the artery, and removal of the
predilatation balloon, followed by passage of the stent deployment
device through the same area of steriosis. This manipulation of the
balloon and then the stent within the narrowed artery, which
contains irregular and friable plaque, can cause thromboembolic
complications. (Friable plaque has the gross pathological
appearance of degenerated, loose, fibroatheromatous debris. For
example, dislodgment of a fragment of plaque can cause a stroke if
it is not caught before it passes into the brain.)
[0006] Hence, it is desirable to provide a device that requires
minimal manipulation within the area of a stenosis. It is further
desired to provide a device that is capable of preventing any
fragments of plaque that may become dislodged from passing up
through the artery and into the brain. For friable or thrombotic
stenoses, the covered stent of the present invention offers the
benefit of holding the thrombus or friable material up against the
vessel wall, and preventing prolapse through the open space between
stent struts and potential embolism downstream. (A thrombus can be
viewed as a clot--red blood cells held together by fibrin--that
adheres to the wall of a blood vessel.) Thrombosis has been
described as coagulation occurring in the wrong place or at the
wrong time. The end result of thrombosis is an obstruction of the
blood flow.
[0007] Several things can happen after a thrombus forms. The
fibrinolytic system may completely degrade the clot allowing blood
flow to return to normal. The thrombus may "propagate"--accumulate
more fibrin and platelets and grow along the course of the vessel.
The thrombus may become fibrotic and be incorporated into the wall
of the blood vessel. In some cases new blood vessels may grow into
the fibrotic thrombus and establish partial but reduced blood flow
(recanalization). Thrombi may dislodge and travel to other sites in
the circulation (thromboembolus). The major clinical consequences
of thrombus formation are narrowing and occlusion of blood vessels,
or the generation of an embolus. Both of these can lead to tissue
ischemia or infarct.
[0008] Although a number of different designs for stents have been
published, stents are generally configured as elongate cylindrical
structures that are provided in a first state and can assume a
second, different state, with the second state having a
substantially greater diameter than the first state. A stent is
implanted in a patient using an appropriate delivery system for the
type of stent being implaced within the patient's arterial system.
There are two basic types of stents--those that are expanded
radially outward due to the force from an inflated angioplasty type
balloon, such as the, Palmaz-Schatz.RTM. stent, and those that are
self expanding, the SMART.RTM. nitinol stent (made of a nickel
titanium alloy)
[0009] Stents may be used in combination with a PTCA procedure.
Specifically, stents are sometimes used following a PTCA procedure
if the artery is totally occluded or if the lesions have occluded a
previously placed surgical graft. Typically, a stent constrained
within an introducer sheath is 20 advanced to a site within the
patient's artery through a guide catheter. For the balloon-expanded
type, after the introducer sheath is retracted, a balloon disposed
inside the stent is inflated to a pressure ranging from about six
to fourteen atmospheres. The force produced by the inflated balloon
expands the stent radially outward beyond its elastic limit,
stretching the vessel and 25 compressing the lesion to the inner
wall of the vessel. A self-expanding stent expands due to spring
force following its implacement in the artery, after a restraining
sheath is retracted from the compressed stent, or in the case of
the nitinol version, the stent assumes its expanded memory state
after being warmed above the martensitic transition temperature for
the nitinol alloy (e.g., above 30.degree. C.)
[0010] Following the expansion process, when the balloon catheter
is used, the balloon is removed from inside the stent and the
catheter and other delivery apparatus is withdrawn. The lumen
through the vessel is then substantially increased, improving blood
flow. After a stent or other endoluminal device is implanted, a
clinical examination and either an angiography or an ultrasonic
morphological procedure is performed to evaluate the success of the
stent emplacement procedure in opening the diseased artery or
vessel. These tests are typically repeated periodically, e.g., at
six-month intervals, since restenosis of the artery may sometimes
occur.
[0011] Implantable devices may be used in other contexts, such as
for abdominal aortic aneurysms. The abdominal aortic aneurysm
usually arises in the infrarenal portion of the diseased aorta, for
example, below the kidneys. When left untreated, the aneurysm may
eventually cause rupture of the sac with ensuing fatal hemorrhaging
in a very short time. High mortality associated with the rupture
led initially to transabdominal surgical repair of abdominal aortic
aneurysms. Surgery involving the abdominal wall, however, is a
major undertaking with associated high risks. There is considerable
mortality and morbidity associated with this magnitude of surgical
intervention, which in essence involves replacing the diseased and
aneurysmal segment of blood vessel with a prosthetic device,
typically is a synthetic tube, or graft, usually fabricated of
polyester, Urethane, DACRON, TEFLON, or other suitable material,
such as those disclosed in U.S. Pat. No. 5,998,024 (issued Dec. 7,
1999).
[0012] Generally, stents, grafts, and graft stents are implantable
medical devices (sometimes termed implantable tubular prostheses)
placed within blood vessels and other body passageways to treat
disease conditions such as stenoses, occlusions, and aneurysms.
Transluminal implantation of such devices requires that they be
introduced to the site collapsed about or within an introduction
device and released to self expand or are expanded by other
mechanisms to an expanded tubular state providing a lumen of
approximately the same size as the patent vessel or duct lumen.
[0013] Stents can be viewed as scaffoldings, of generally
cylindrical symmetry, that function to physically support, and, if
desired, expand the wall of the passageway. Typically, a stent
consists of two or more struts or wire support members connected
together into a lattice-like or open weave frame. Most stents are
compressible for insertion through small cavities, and are
delivered to the desired implantation site percutaneously via a
catheter or similar transluminal device. Once at the treatment
site, the compressed stent is expanded to fit within or expand the
lumen of the passageway. Stents are typically either self-expanding
or are expanded by inflating a balloon that is positioned inside
the compressed stent at the end of the catheter. Intravascular
stents are often deployed after coronary angioplasty procedures to
reduce complications, such as the collapse of arterial lining,
associated with the procedure.
[0014] Stents have a lattice-like structure, leaving spaces defined
by the struts that form the stent. Such spaces can allow plaque
from the lesion to fall through the stent and enter the blood
stream during stent deployment. The spaces can also permit
malignant tissue growth through the stent openings into the body
passageway and can allow undesired contact between blood flowing
through the blood vessel and damaged portions of the vessel.
Covered stents, in which a polymeric material surrounds and is
attached to the stent, have been proposed to alleviate the concerns
associated with stent openings.
[0015] Diseased vessels are also treated with grafts. Grafts are
generally tubular in morphology and are used to replace or create
an anatomical passageway to provide a new conduit for fluid, e.g.
blood. Grafts are often made from a portion of a vein, but can also
be constructed from a synthetic material to form a synthetic graft.
Like stents, synthetic grafts often are positioned percutaneously
via a catheter, for instance, to be placed at the site of an
aneurysm to prevent further dilation and possible rupture of the
diseased vessel.
[0016] In certain instances, the graft material alone does not
provide enough structural support for the graft, causing the graft
to collapse and occlude or impede the flow of blood through the
vessel. Grafts may be used with stents. Specifically, a graft may
comprise a tube-shaped member having an inside diameter only
slightly larger than the circumference of the deployed stent. The
graft may be made of latex, silicone, polytetraflouroethylene,
polyethylene, Dacron polyesters, polyurethane or other suitable
biocompatible material. The graft material must be flexible and
durable, so that it can withstand the effects of installation and
usage. Depending on the material chosen, it may be preferable to
form the graft in one of several ways. For example, the graft may
be extruded, woven or formed by dipping a substrate in the desired
material, removing the material from the substrate, and trimming
the end of the material, so as to form a cylindrical tube having an
opening at each end.
[0017] The graft is deployed simultaneously with the deployment of
the stent. Prior to deployment, the graft is collapsed, with the
collapsed stent inside or outside of it. As described, the stent
and graft may then be inserted into a catheter, deployed, and
expanded by pressurization of a balloon. A graft deployed and
supported in this manner may be used to seal an aneurysm or similar
defect in a vessel. The tissue of the vessel adjacent to the graft
will grow onto the graft, so that the graft becomes an integral,
reinforcing that part of the vessel wall and helping to reduce the
risk of future ruptures at that location. For those cases wherein
the material is synthetic, the combined structure is sometimes
referred to as a synthetic stent graft. Stents are also placed at
the ends of synthetic grafts to help secure the ends of the
synthetic graft to vessel walls.
[0018] As a point of nomenclature, the term "stent" is sometimes
used interchangeably in the prior art with "graft." In the present
invention, the graft and the stent are separate elements. Of
grafts, one has species of vascular grafts and artificial grafts.
Vascular grafts classically are longer and have more continuous
sidewalls than the purely metal stent. The expression "vascular
graft" originally was used to described harvested blood vessels
used to bypass a length of diseased or enlarged blood vessel, and
the expression "artificial graft" typically connotes an elongated,
biocompatible, tubular body mimicking the flexibility of the
natural blood vessel it is intended to replace. In an open chest
surgical procedure, the active attachment of such flexible vascular
or artificial grafts to patent blood vessel ends is effected by
suturing in a procedure referred to as anastomosis.
[0019] A challenge to the use of covered stents and synthetic stent
grafts is keeping the stent covering attached to the stent. During
expansion of the prosthesis, the covering and the stent have
different expansion versus length properties, causing the cover to
possibly detach from the stent, or bunch, creating an irregular
blood flowpath which can adversely affect graft patency. Currently,
covers are attached to stents by stitching or gluing, or by wholly
embedding the stent into the polymeric cover material. When
stitches are used, the cover is typically punctured at the stitch
site, leaving an opening and a weak place in the cover that may
tear or rip when the covered stent is expanded. Further, the act of
suturing through the fabric creates potential leak paths for the
blood. The present invention avoids attachment that breaches the
graft material.
[0020] Separately in the prior art, using glue instead of stitches
addresses the puncture problems, however, glue can be difficult to
keep in place on the stent when attaching the cover material.
Furthermore, in some cases, the glue itself does not provide a
strong enough hold to keep the cover attached. When the stent is
wholly embedded into the cover material, the covering is on both
the inside and outside of the stent and may cause the profile of
the covered stent to be larger than desired.
[0021] Another concern with wholly embedded stents is that crimping
of the stent into a small profile for delivery becomes more
difficult, as the cover material cannot fold independently from the
stent, and becomes pinched in between the collapsing stent strut
architecture. This prevents minimization of the crimped profile.
Specifically, the present invention pertains to a manner of
attaching the graft to the stent.
[0022] The present invention overcomes any difficulties associated
with the current art related to the joining of the graft to the
stent and to movement of the graft from the stent.
SUMMARY OF THE INVENTION
[0023] The present invention is generally directed to a stent
design in which there is a covered stent comprising individual
stent rings alternately loaded inside and outside of the covering
material.
[0024] The present invention specifically has the advantages of
holding the covering in place without double radial layers of metal
or adhesives; holding cover material up from draping into the
lumen; minimizing stent lengthening during crimping, because each
ring acts independently (stent lengthening presents concerns during
crimping of the covered stent.); maximizing stent flexibility
(because there are no bridges, the covering determines the flexing
force between segments).
[0025] The present invention comprises embodiments in which the
covering is ePTFE or PET (DACRON); in which stent spacing is varied
to optimize flexure properties; in which oversizing of internal
stents is varied to the covering in order to maximize the fixation
force at the ends; in which some of the uncovered stent is left to
stick out of the end of covering to aid in anchoring the vessel; in
which the internodal distance is varied (for embodiments employing
ePTFE as a covering); in which the stent strength of internal
versus external stents is varied, most particularly the embodiment
with stronger internal stents.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] FIG. 1 Is a side plan view of the stent graft of the present
invention;
[0027] FIG. 2 is a cross sectional view of the stent graft of the
present invention taken along lines 2-2 of FIG. 1; and
[0028] FIG. 3 is a cross sectional view of the stent graft of the
present invention taken along lines 3-3 of FIG. 1.
DETAILED DESCRIPTION OF THE INVENTION
[0029] The present invention is directed to a covered stent graft
10 comprised of individual stent rings 20 alternately loaded inside
25 and outside 30 of a covering material 40. The rings 20 supply
radial strength. individually, but the rings are not connected to
adjacent rings longitudinally.
[0030] The present invention is in the general art of stent grafts.
Stent grafts are useful in treating two conditions--aneurysmal
disease and thrombotic or friable stenotic lesions. For aneurysmal
disease, the stent graft 10 is covered with a material 40
(typically DACRON or expanded polytetrafluoroethylene ("ePTFE")
which allows the stent to span the aneurysmal vessel segment and to
seal blood flow and pressure from reaching the aneurysmal sac. The
fabric covering 40 typically is porous, but with small enough pores
to coagulate acutely and to exclude the aneurysm from the
transmitted blood pressure. Once the aneurysm is excluded, the sac
is expected to shrink in size, and the risk of rupture is
eliminated.
[0031] In the aneurysmal application, the main part of the stent
graft 10 is "floating" in free space with only proximal and distal
ends sealing rings 25, 30 against the healthy vessel segments
adjacent to the aneurysm.
[0032] For friable or thrombotic stenoses, a covered stent graft 10
may offer the benefit of holding the thrombus or friable material
up against the vessel wall, and preventing prolapses through the
open space between stent struts, and potential embolism
downstream.
[0033] Separately, there are problems in the repair of many
abdominal aortic aneurysms. One such problem is that the aneurysm
neck is often too short to permit adequate fixation with an
expandable stent. (Generally, a length of two centimeters or more
is needed for adequate anchoring of the graft.) Additionally, the
aneurysm neck is frequently too heavily calcified to permit
fixation with hooks, i.e., the hooks cannot penetrate areas of the
aortic wall that have thick, calcified plaques. In other cases, the
inner wall of the neck is thickened by soft, friable plaque or
thrombus that makes fixation with hooks impossible or
inadequate.
[0034] In the application for friable or thrombotic stenoses, the
stent graft 10 opposes the vessel wall with rings 25, 30 along its
entire length. This alignment is distinct from that found in the
aneursymal application.
[0035] In terms of background, a graft is a typically a fabric or a
covering. A stent is a structural element that supports the graft.
Historically, grafts have been surgically implanted as substitutes
for native vessels. The technology of stent grafts began with
surgical grafts being supported endoluminally with early vascular
stents. A problem solved by the present invention, is the poor
connection between graft and stent found in prior art embodiments
of stent grafts. An objective is to have stent grafts to evolve to
become a composite of the two elements.
[0036] Many of the prior art devices have stent segments attached
to the graft material with sutures. The need to make flexible
structures has led the art to the use of segmented rigid stents,
which articulate at the unsupported graft areas. In order to keep
the segmented stents in place, such stents employ attachment to the
graft fabric. The act of suturing through the fabric creates
potential leak paths for the blood. The present invention avoids
attachment that breaches the graft material.
[0037] Separately, an alternate method of fixing the graft to the
stent is to sandwich a layer of graft between two stents. This
sandwiching creates a large crimped profile. The present invention
avoids both suturing and multiple stent layers at the same
longitudinal location.
[0038] Generally, the present invention offers the following
advantages:
[0039] 1. No through graft perforations for fixation of material to
the stent.--Perforations of the covering material are undesirable
when trying to seal aneurysms. The present invention uses friction
from alternating inside and outside segments to join the covering
and the stent.
[0040] 2. No double walls of material, as in stent "sandwiches", so
that the profile is minimized.--The present invention allows graft
material to move with respect to stents during crimping, which
prevents pinching of the graft by the stent during crimping. In the
prior art, longitudinally connected stents change length during
crimping, but the graft does not change its length. The present
invention reduces foreshortening of the stent overall versus a
fully longitudinally connected stent.
[0041] The present invention minimizes, or eliminates, the need for
staples or sutures for the attachment of the graft material to the
stent. The act of suturing through the covering fabric is
undesirable because it creates leak paths for the blood. The use of
coating decreases flexibility.
[0042] In the prior art, stents are placed inside of graft tubes,
and held in place by the force of the stent against the vessel
wall. A desired structural graft is a composite material with the
properties of both a graft and a stent.
[0043] It is an object of the present invention to assemble a woven
DACRON (also denoted PET OR PETE), or TEFLON or other biocompatible
graft material to a stent, while allowing for folding and
compressibility of the graft semi-independently of the stent, yet
still held in a multitude of locations to provide for good stent to
graft apposition (movement together). Sometimes the following
materials will be used: ePTFE, PET, UHMWPE (ultra high molecular
weight polyethylene), polyester polyarylate, and PEEK (polyester
ether ketone). Some prior art devices depend on manual sewing to
define these stent to graft attachment points. The present
invention allows for an advancement to eliminate the costly
manufacturing technique of the prior art.
[0044] The covering of the present invention may be woven polyester
made with mono or multi-filament yarn. The covering may comprise
TEFLON. The covering may comprise DACRON.
[0045] The invention resolves other-problems in the prior art. Thin
walled plastic stent grafts of the prior art can change diameter by
wrinkling or folding. When the stent graft is fully open, the
perimeter fabric is taut. When it is loaded into a catheter, the
perimeter fabric folds in on itself (like a pleated skirt). A
nitinol stent, or even a malleable steel stent, changes diameter
through strut bending. Although the graft fibers also bend, they
will bend out of plane, towards and away from the centerline of the
graft. The stent struts bend within the circumference as the device
diameter changes.
* * * * *